Acute diarrhoeal illness remains a common medical problem in children with nearly 1.7 billion cases globally every year. We report five infants who, following severe diarrhoea, developed methaemoglobinemia. This is an altered state of haemoglobin presenting with cyanosis and can pose a diagnostic dilemma. It should be suspected in young infants without cyanotic heart disease presenting with severe diarrhoea, sepsis and cyanosis disproportionate to their clinical status. Its outcome depends on prompt treatment, the severity of underlying sepsis and co-morbidity.